Novatel OEM719, Инструкция по установке и эксплуатации

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Chapter 3 OEM7 Receiver Operation
OEM7 Installation and Operation User Manual v4 67
each subframe is 300 bits in length. With the 50 Hz data bit rate there is a new subframe trans-
mitted every six seconds.
3.10.2 Time Definitions
The following are related definitions:
Coarse Time
Each subframe contains the transmit time of the next subframe in seconds of GPS Time of Week
(TOW). After the first subframe is collected and decoded by the receiver, an approximate cal-
culation of the receiver clock offset can be made. The receiver clock offset is the difference
between GPS time and internal receiver time. The calculation is based on subframe transmit
time and the approximate propagation time from the satellite signal to the receiver. The position
of the satellite and receiver clock offset are used to re-initialize the seconds counter on the
receiver, resulting in receiver/GPS time synchronization. The accuracy of the receiver time is
expected to be within 30 milliseconds (ms) of GPS time. This initial synchronization is referred
to as coarse time and is indicated by COARSE in the time status field of the
TIMESYNC log.
Fine Time
When at least four satellites are acquired to calculate the antenna position, a more accurate
estimate of the receiver clock offset is calculated. The new receiver clock offset is used to syn-
chronize the receiver clock even closer to GPS time. This is referred to as fine time and appears
as FINE or FINESTEERING in the time status field of the
TIMESYNC log. Fine time accuracy is a
function of the GPS constellation status and is influenced by external receiver RF delay. For the
Standard Position Service (SPS) the time accuracy is specified as 20 ns (1 sigma) with internal
compensation.
Fine Clock
An OEM7 receiver that is tracking satellites and has a FINE or FINESTEERING receiver clock
state.
Cold Clock
An OEM7 receiver that needs to have its clock synchronized with the Fine receiver. It may have
any clock state (except FINE or FINESTEERING) that includes UNKNOWN.
Warm Clock
An OEM7 receiver that has its clock adjusted to greater than 500 ms. Refer to the TIME log to
view the clock offset.
The OEM7 Commands and Logs Reference Manual contains details of the logs mentioned
above.
3.10.3 Procedures to Transfer Time
These procedures are used to transfer time between a fine clock and a cold or warm clock GPS
receiver.
When connecting two receivers to transfer time, disable responses on the COM port
used to connect the receivers by issuing the following command on both receivers:
interfacemode comX novatel novatel none
Where comX is the port used on the receiver.